Dendrimer solid acid and polymer electrolyte membrane including the same

ABSTRACT

Provided are a dendrimer solid acid and a polymer electrolyte membrane using the same. The polymer electrolyte membrane includes a macromolecule of a dendrimer solid acid having ionically conductive terminal groups at the surface thereof and a minimum amount of ionically conductive terminal groups required for ionic conduction, thus suppressing swelling and allowing a uniform distribution of the dendrimer solid acid, thereby improving ionic conductivity. Since the number of ionically conductive terminal groups in the polymer electrolyte membrane is minimized and the polymer matrix in which swelling is suppressed is used, methanol crossover and difficulties of outflow due to a large volume may be reduced, and a macromolecule of the dendrimer solid acid having the ionically conductive terminal groups on the surface thereof is uniformly distributed. Accordingly, ionic conductivity is high and thus, the polymer electrolyte membrane shows good ionic conductivity even in non-humidified conditions.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2005-0094934, filed on Oct. 10, 2005, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein in its entirety by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a dendrimer solid acid and a polymerelectrolyte membrane using the same, and more particularly, to adendrimer solid acid which provides high ionic conductivity and apolymer electrolyte membrane with excellent ionic conductivity and lowmethanol crossover.

2. Description of the Related Art

A fuel cell is an electrochemical device which directly transformschemical energy of oxygen and hydrogen contained in a hydrocarbonmaterial such as methanol, ethanol, or natural gas into electric energy.

Fuel cells can be classified into Phosphoric Acid Fuel Cells (PAFC),Molten Carbonate Fuel Cells (MCFC), Solid Oxide Full Cells (SOFC),Polymer Electrolyte Membrane Fuel Cells (PEMFC), and Alkaline Full Cells(AFC) according to the type of electrolyte used. All fuel cells operateon the same general principles, but may differ in the type of fuel used,the operating temperature, the catalyst used or the electrolyte used. Inparticular, a PEMFC can be used in small-sized stationary powergeneration equipment or a transportation system due to its low operatingtemperature, high output density, rapid start-up, and prompt response tothe variation of output demand.

The core part of a PEMFC is a Membrane Electrode Assembly, MEA. An MEAgenerally comprises a polymer electrolyte membrane and two electrodes onopposite sides of the polymer electrolyte membrane which independentlyact as a cathode and an anode.

The polymer electrolyte membrane acts as a separator, blocking directcontact between an oxidizing agent and a reducing agent, andelectrically insulates the two electrodes while conducting protons.Accordingly, a good polymer electrolyte membrane has high protonconductivity, good electrical insulation, low reactant permeability,excellent thermal, chemical and mechanical stability under normalconditions of fuel cell operation, and a reasonable price.

In order to meet these requirements, various types of polymerelectrolyte membranes have been developed, and, in particular, a highlyfluorinated polysulfonic acid membrane such as a NAFION™ membrane hasbeen shown to exhibit good durability and performance. However, aNAFION™ membrane should be sufficiently humidified, and to preventmoisture loss, the NAFION™ membrane should be used at a temperature of80° C. or below. Also, since, a carbon-carbon bond of a main chain isattacked by oxygen (O₂), a NAFION™ membrane may not be stable under theoperating conditions of a fuel cell.

Moreover, in a Direct Methanol Fuel Cell (DMFC), an aqueous methanolsolution is supplied as a fuel to the anode and a portion of unreactedaqueous methanol solution permeates the polymer electrolyte membrane.The methanol solution that permeates the polymer electrolyte membranecauses a swelling phenomenon in an electrolyte membrane and diffuses toa cathode catalyst layer. Such a phenomenon is referred to as “methanolcrossover,” and can lead to the direct oxidization of methanol at thecathode where an electrochemical reduction of hydrogen ions and oxygenoccurs, and thus the methanol crossover results in a drop in theelectric potential of the cathode, thereby causing a significant declinein the performance of the fuel cell.

This same fuel crossover problem may also arise with other fuel cellsusing a liquid polar organic fuel other than methanol.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a dendrimer solidacid is provided which can provide ionic conductivity to a polymerelectrolyte membrane while not separating easily from the polymerelectrolyte membrane.

According to another embodiment of the present invention, a polymerelectrolyte membrane is provided which includes a dendrimer solid acidwhich shows excellent ionic conductivity, even without humidifying, andlow methanol crossover.

According to another embodiment of the present invention, a MembraneElectrode Assembly (MEA) is provided that includes an improved polymerelectrolyte membrane.

According to another embodiment of the present invention, a fuel cell isprovided including an improved polymer electrolyte membrane.

According to an embodiment of the present invention, a dendrimer solidacid of Formula 1 is provided:

where X is a core represented by one of Formula 2 through Formula 17:

where a is an integer from 1 to 6 corresponding to the number of bondingsites of X, n is an integer from 2 to 6 corresponding to the number ofgenerations of branching units in the dendrimer, each of E₁ throughE_(n−1) is an organic group independently selected from the organicgroups represented by Formula 18 through Formula 22:

and E_(n) is H, —OH, —COOH, —SO₃H, or —OPO(OH)₂.

According to another embodiment of the present invention, a polymerelectrolyte membrane is provided that includes at least one polymermatrix having an end group selected from the group consisting of —SO₃H,—COOH, —OH, and —OPO(OH)₂ at the terminal of a side chain, with adendrimer solid acid as set forth above uniformly distributed throughthe polymer matrix.

According to another embodiment of the present invention, a MembraneElectrode Assembly (MEA) is provided including: an improved electrolytemembrane including a polymer electrolyte membrane as set forth above; acathode on one side of the Membrane Electrode Assembly having a catalystlayer and a diffusion layer; and an anode on the other side of theMembrane Electrode Assembly having a catalyst layer and a diffusionlayer.

According to another embodiment of the present invention, a fuel cell isprovided including an improved Membrane Electrode Assembly (MEA) as setforth above.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a graph showing the results of a Nuclear Magnetic Resonance(NMR) analysis performed to identify the structure of a precursor of adendrimer solid acid according to an embodiment of the presentinvention;

FIG. 2 is a graph showing the results of a Fourier Transform InfraredSpectroscopy (FT-IR) analysis performed to identify the structure of adendrimer solid acid according to an embodiment of the presentinvention;

FIG. 3 is a schematic illustration of a Membrane Electrode Assembly(MEA) according to an embodiment of the invention; and

FIG. 4 is a schematic illustration of a fuel cell system according to anembodiment of the invention.

DETAILED DESCRIPTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. The invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art.

A dendrimer solid acid according to an embodiment of the presentinvention is represented by Formula 1 below.

where X is a core represented by one of Formula 2 through Formula 17,

where a is an integer from 1 to 6 corresponding to the number of bondingsites of X, n is an integer from 2 to 6 corresponding to the number ofgenerations of branching units of the dendrimer, each of E₁ throughE_(n−1) is an organic group independently selected from the organicgroups represented by Formula 18 through Formula 22:

and E_(n) is H, —OH, —COOH, —SO₃H, or —OPO(OH)₂.

The term “dendrimer” refers to a single macromolecule having a branchedshape which is well arranged so as to be substantially two-dimensionallyor three-dimensionally symmetrical. Certain dendrimers can be classifiedas cone or sphere forms. A dendrimer is similar to a polymer in thatboth have large molecules with a large molecular weight, but unlike ageneral polymer having a linear shape, a dendrimer has a symmetricalring shape and is formed of a single macromolecule having nodistribution of molecular weight. The dendrimer has characteristics ofboth a monomer and a polymer, and thus can have various applications.

It should be apparent to one of skill in the art that the individualbranches of the dendrimer of Formula 1 are not limited to straight chainbranches, but rather, each branch may have further branches depending onthe number of E_(i+1) bonding sites for a particular E_(i)organic groupat the i^(th) level of the dendrimer.

In addition, the structure of the dendrimer can be formed by a synthesismethod, for example, a convergent or divergent method. A center portionof the dendrimer is blocked from the outside or is nearly isolated, andthus, various metallic ions or unique functional groups can beprotected. Also, the surface of the dendrimer is three dimensional andlarge so as to be useful for diverse purposes.

If the dendrimer solid acid according to an embodiment of the presentinvention is distributed between polymer matrixes, an outflow due toswelling hardly occurs because the dendrimer solid acid has asignificantly large size. Also, the dendrimer solid acid according to anembodiment of the present invention provides ionic conductivity to apolymer electrolyte membrane since acidic functional groups such as—COOH, —SO₃H, or —OPO(OH)₂ are attached to terminal ends providing highionic conductivity.

A dendrimer solid acid according to an embodiment of the presentinvention may be a compound represented by one of Formulas 23 through26.

Hereinafter, the dendrimer solid acid according to an embodiment of thepresent invention will be described in greater detail with reference toa process of manufacturing the dendrimer solid acid represented byReaction Schemes 1, 2 and 3. The method is provided to facilitate theunderstanding of the present invention, but the present invention is notlimited by the reaction schemes set forth herein. 58314/L550

First, as shown in Reaction scheme 1, one generation of a repeating unitis synthesized.

Then, as shown in Reaction Scheme 2, two generations of the repeatingunit can be synthesized using the repeating unit synthesized in ReactionScheme 1.

As shown in Reaction Scheme 3, the two generations of the repeating unitmanufactured in Reaction Scheme 2 are reacted with a core material belowto manufacture a solid acid precursor.

The solid acid precursor manufactured as described above reacts withsulfuric acid and fumed sulfuric acid to produce the dendrimer solidacid represented by Formula 24. In order to increase the number ofgenerations of the repeating unit, the process shown in Reaction Scheme2 may be repeated.

Moreover, in order to have a functional group such as —COOH, —OH, or—OPO(OH)₂ at the terminal of the dendrimer solid acid, a method ofintroducing an acid functional group such as —SO₃H after manufacturingthe dendrimer is not appropriate. Instead, a structure in which afunctional group such as —COOH, —OH, or —OPO(OH)₂ is protected by analkyl group when synthesizing the first generation of repeating unit isobtained. That is, the functional group is included in a benzyl halidecompound having a structure of —COOR, —OR, or —OPO(OR)₂. The finaldendrimer having the structure with the plurality of generations of therepeating unit is prepared and then the dendrimer solid acid can bemanufactured by detaching an alkyl group. Here, R is, for example, amonovalent C₁₋₅ alkyl group.

A polymer electrolyte membrane according to an embodiment of the presentinvention will now be described.

A polymer electrolyte membrane according to an embodiment of the presentinvention includes at least one polymer matrix having an end groupselected from the group consisting of —SO₃H, —COOH, —OH, and —OPO(OH)₂at the terminal of a side chain and a dendrimer solid acid uniformlydistributed through the polymer matrixes.

The polymer matrix may be a polymer material such as polyimide,polybenzimidazole, polyethersulfone, or polyether-ether-ketone.

The polymer electrolyte membrane according to an embodiment of thepresent invention has good ionic conductivity since the dendrimer solidacid according to an embodiment of the present invention is uniformlydistributed throughout the polymer matrix. That is, acidic functionalgroups at the terminal of the side chain of the polymer matrix andacidic functional groups on the surface of the dendrimer solid acidinteract together to provide high ionic conductivity.

Conventionally, a large amount of jonically conductive terminal groupssuch as sulfone groups are attached to a polymer in a conventionalpolymer electrolyte membrane, but such a configuration may causeswelling. However, in certain polymer matrixes according to the presentinvention, a smaller amount of ionically conductive terminal groups arerequired for ionic conduction, thereby reducing swelling caused bymoisture.

In particular, the polymer matrix herein may be a polymer resinrepresented by Formula 27 below:

where M is a repeating unit of Formula 28 below,

where Y is a tetravalent aromatic organic group or aliphatic organicgroup, and Z is a bivalent aromatic organic group or aliphatic organicgroup; and X of Formula 27 is a repeating unit of Formula 29 below,

where Y′ is a tetravalent aromatic organic group or aliphatic organicgroup, Z′ is a tetravalent aromatic organic group or aliphatic organicgroup, each of j and k is independently an integer from 1 to 6, and R₁is one of —OH, —SO₃H, —COOH, and —OPO(OH)₂.

In addition, m and n are each independently in the range of 30 to 5000,where the ratio of m to n is between 2:8 and 8:2, for example, between3:7 and 7:3, and preferably between 4:6 and 6:4. When the ratio of m ton is less than 2:8, swelling and methanol crossover due to water areincreased. When the ratio of m to n is greater than 8:2, hydrogen ionconductivity is too low to secure an optimum level of hydrogen ionconductivity even when the solid acid is added.

For example, M and X, which are repeating units of the polymer resin inFormula 27, may have the structures represented by Formula 30 andFormula 31, respectively:

where R₁, j and k are defined as in Formula 29.

The process of manufacturing the polymer matrix according to Formula 27is not particularly restricted, and may be processed illustrated inReaction Scheme 4.

A Membrane Electrode Assembly (MEA) including the polymer electrolytemembrane according to an embodiment of the present invention will now bedescribed with reference to FIG. 3. The MEA includes: an electrolytemembrane 130 including a polymer electrolyte membrane according to anembodiment of the present invention; a cathode 50 on one side of theelectrolyte membrane 130 having a catalyst layer 53 and a diffusionlayer 51, and an anode 30 on the other side of the electrolyte membrane130 having a catalyst layer 33 and a diffusion layer 31. Cathodes andanodes, each having a catalyst layer and a diffusion layer are wellknown in the field of fuel cells. The polymer electrolyte membraneaccording to an embodiment of the present invention can be usedindependently as an electrolyte membrane or can be combined with anothermembrane having ionic conductivity.

A fuel cell including the polymer electrolyte membrane will now bedescribed.

The fuel cell includes: an electrolyte membrane including the polymerelectrolyte membrane according to an embodiment of the present inventionas described above; a cathode on one side of the electrolyte membranehaving a catalyst layer and a diffusion layer; and an anode on the otherside of the electrolyte membrane having a catalyst layer and a diffusionlayer. Each of the cathode and anode has a catalyst layer and adiffusion layer as is well known in the field of fuel cells. The polymerelectrolyte membrane according to an embodiment of the present inventioncan be used independently as an electrolyte membrane or can be combinedwith another membrane having ionic conductivity.

A representative fuel cell system according to an embodiment of theinvention is shown in FIG. 4. The fuel cell system 100 includes a fuelsupplier 1, an oxygen supplier 5, and a fuel cell stack 7. The fuelsupplier 1 includes a fuel tank 9 for containing a fuel such as methanoland a fuel pump 11 for supplying the fuel to the stack 7. The oxygensupplier 5 includes an air pump 13 for supplying oxygen from air to thestack 7. The stack includes a plurality of electricity generating units19, each comprising a Membrane Electrode Assembly 21 and separators 23and 25. Each Membrane Electrode Assembly 21 comprises a polymerelectrode member with an anode on a first side and a cathode on a secondside. To manufacture the fuel cell, a conventional method can be used,and thus, a detailed description is omitted herein.

The polymer electrolyte membrane according to an embodiment of thepresent invention uses a minimal number of ionically conductive terminalgroups required for ionic conduction, and uses a polymer matrix in whichswelling is suppressed without a significant effect on methanolcrossover and the difficulties of outflow caused by a large number ofionically conductive terminal groups while uniformly distributing alarge sized dendrimer solid acid having ionically conductive terminalgroups on the surface of the dendrimer solid acid. Accordingly, ionicconductivity is greatly improved, and thus, polymer electrolytemembranes according to certain embodiments of the present invention showgood ionic conductivity, even in non-humidified conditions.

The present invention will be described in greater detail with referenceto the following examples. The following examples are for illustrativepurposes only, and are not intended to limit the scope of the invention.

EXAMPLE 1 Manufacturing the Compound of Formula 23

0.01 moles of 1,1,1-tri(4-hydroxyphenyl)-methane, 0.033 moles of arepeating unit manufactured according to Reaction Scheme 2, 0.033 molesof K₂CO₃, and 9 mmol of 18-crown-6 were dissolved in acetone containedin a 3 neck reaction flask equipped with a mixer under a nitrogenatmosphere, and reacted for 16 hours at 60° C. When the reaction wascomplete, acetone was removed with an evaporator and the resultingproduct was dissolved again in ethylacetate.

Then, unreactive hydroxy compounds were extracted with a separatingfunnel using a NaOH aqueous solution, moisture was removed using MgSO₄from an ethylacetate solution in which the product was dissolved, andthe solvent was removed by evaporating. Then, the product was columnrefined using toluene to obtain a solid acid precursor of Formula 32.The structure of the solid acid precursor was identified using NuclearMagnetic Resonance (NMR) analysis, and the results are shown in FIG. 1.

Then 5 g of the dendrimer solid acid precursor of Formula 32 wascompletely dissolved in 15 ml of sulfuric acid, and 5 ml of fumedsulfuric acid (SO₃ 60%) was added thereto. The mixture was reacted at80° C. for 12 hours and precipitated in ether. The precipitate wasfiltered and then dissolved in water. The product was put into adialysis membrane and refined to obtain the compound of Formula 23. Thestructure of the compound of Formula 23 was identified using FourierTransform Infrared Spectroscopy (FT-IR) analysis, and the results areshown in FIG. 2.

EXAMPLE 2 Manufacturing the Compound of Formula 24

The compound of Formula 24 was manufactured in the same manner as thecompound of Formula 23 in Example 1, except that(4-hydroxyphenyl)-(2,3,4-trihydroxyphenyl)methanone was used instead of1,1,1-tri(4-hydroxyphenyl)-methane.

EXAMPLE 3 Manufacturing the Compound of Formula 25

The compound of Formula 25 was manufactured in the same manner as thecompound of Formula 23 in Example 1, except that2,2-bis(4-hydroxy-3-methyl phenyl)propane was used instead of1,1,1-tri(4-hydroxyphenyl)-methane.

EXAMPLE 4 Manufacturing the Compound of Formula 26

The compound of Formula 26 was manufactured in the same manner as thecompound of Formula 23 in Example 1, except that1,1,1-tri(4-hydroxyphenyl)-ethane was used instead of1,1,1-tri(4-hydroxyphenyl)-methane.

EXAMPLE 5

100 parts by weight of the polymer matrix of Formula 27 (M: Formula 30,N: Formula 31), the ratio of m to n being 5:5, and 10 parts by weight ofthe dendrimer solid acid of Formula 23 were completely dissolved inN-metylpyrrolidone (NMP) and cast to manufacture a polymer electrolytemembrane.

The ionic conductivity and methanol crossover were respectively measuredfor the polymer electrolyte membrane manufactured in Example 5 and apolymer membrane in which solid acid was not included. The results areillustrated in Table 1. TABLE 1 Ionic conductivity Methanol crossover(S/cm) (cm²/sec) Polymer membrane 2.60 × 10⁻⁶ 2.73 × 10⁻⁹ Example 5 5.18× 10⁻⁴ 5.09 × 10⁻⁸ (after 20 minutes) 2.04 × 10⁻⁴ (after 1 day) 4.40 ×10⁻⁴ (after 2 days)

As illustrated in Table 1, by adding the dendrimer solid acid accordingto an embodiment of the present invention, the methanol crossover isslightly increased and the ionic conductivity is increased much morethan the methanol crossover. Therefore, when the solid acid according toan embodiment of the present invention is used, ionic conductivity maybe greatly improved without significantly affecting methanol crossover.

EXAMPLE 6 AND EXAMPLE 7

Polymer electrolyte membranes were manufactured in the same manner as inExample 5, except that 5 parts by weight and 15 parts by weight of thedendrimer solid acid in Formula 23 were respectively used. The ionicconductivity and methanol crossover of the polymer electrolyte membraneswere measured one day after the polymer electrolyte membranes weremanufactured, and the results are shown in Table 2. TABLE 2 Ionicconductivity Methanol crossover (S/cm) (cm²/sec) Example 5 2.04 × 10⁻⁴5.09 × 10⁻⁸ Example 6 1.84 × 10⁻⁵ 8.73 × 10⁻⁹ Example 7 1.02 × 10⁻⁴ 1.56× 10⁻⁸

As illustrated in Table 2, as the amount of the dendrimer solid acidincreases, ionic conductivity improves. The methanol crossover alsoincreases, however, the ion conductivity increases much more.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A dendrimer solid acid of the following formula:

where X is a core represented by one of Formula 2 through Formula 17:

where a is an integer from 1 to 6 corresponding to the number of bondingsites of X, n is an integer from 2 to 6 corresponding to the number ofgenerations of branching units of the dendrimer, each of E₁ throughE_(n−1) is independently selected from the organic groups represented byFormula 18 through Formula 22:

and E_(n) is H, —OH, —COOH, —SO₃H, or —OPO(OH)₂.
 2. The dendrimer solidacid of claim 1, wherein the dendrimer is a compound selected from thegroup consisting of compounds of Formula 23 through Formula 26:


3. A polymer electrolyte membrane comprising the dendrimer solid acid ofclaim 1 and at least one polymer matrix having an end group selectedfrom the group consisting of —SO₃H, —COOH, —OH, and —OPO(OH)₂ at theterminal of a side chain, wherein the dendrimer solid acid is uniformlydistributed through the at least one polymer matrix.
 4. The polymerelectrolyte membrane of claim 3, wherein the polymer matrix is at leastone polymer material selected from the group consisting of polyimide,polybenzimidazole, polyethersulfone, and polyether-ether-ketone.
 5. Thepolymer electrolyte membrane of claim 3, wherein the polymer matrix is apolymer resin represented by Formula 27:

where M is a repeating unit of Formula 28:

where Y is a tetravalent aromatic organic group or aliphatic organicgroup, and Z is a bivalent aromatic organic group or aliphatic organicgroup; and X of Formula 27 is a repeating unit of Formula 29:

where Y′ is a tetravalent aromatic organic group or aliphatic organicgroup, Z′ is a tetravalent aromatic organic group or aliphatic organicgroup, each of j and k is independently an integer from 1 to 6, and R₁is one of —OH, —SO₃H, —COOH, and —OPO(OH)₂; each of m and n isindependently from 30 to 5000; and the ratio of m to n is from 2:8 to8:2.
 6. A Membrane Electrode Assembly (MEA) comprising: the polymerelectrolyte membrane of claim 3; a cathode on a first side of thepolymer electrolyte membrane comprising a catalyst layer and a diffusionlayer; and an anode on a second side of the polymer electrolyte membranecomprising a catalyst layer and a diffusion layer.
 7. The MembraneElectrode Assembly (MEA) of claim 6, wherein the polymer matrix of thepolymer electrolyte membrane comprises at least one polymer materialselected from the group consisting of polyimide, polybenzimidazole,polyethersulfone, and polyether-ether-ketone.
 8. The Membrane ElectrodeAssembly (MEA) of claim 6, wherein the polymer matrix of the polymerelectrolyte membrane comprises a polymer resin represented by Formula27:

where M is a repeating unit of Formula 28:

where Y is a tetravalent aromatic organic group or aliphatic organicgroup, and Z is a bivalent aromatic organic group or aliphatic organicgroup; and X of Formula 27 is a repeating unit of Formula 29:

where Y′ is a tetravalent aromatic organic group or aliphatic organicgroup, Z′ is a tetravalent aromatic organic group or aliphatic organicgroup, each of j and k is independently an integer from 1 to 6, and R₁is one of —OH, —SO₃H, —COOH, and —OPO(OH)₂; each of m and n isindependently from 30 to 5000; and the ratio of m to n is from 2:8 to8:2.
 9. A fuel cell comprising: the polymer electrolyte membrane ofclaim 3; a cathode on a first side of the polymer electrolyte membranecomprising a catalyst layer and a diffusion layer; an anode on a secondside of the polymer electrolyte membrane comprising a catalyst layer anda diffusion layer; a first separator adjacent the cathode; and a secondseparator adjacent the anode.
 10. The fuel cell of claim 9, wherein thepolymer matrix of the polymer electrolyte membrane comprises at leastone polymer material selected from the group consisting of polyimide,polybenzimidazole, polyethersulfone, and polyether-ether-ketone.
 11. Thefuel cell of claim 9, wherein the polymer matrix of the polymerelectrolyte membrane comprises a polymer resin represented by Formula27:

where M is a repeating unit of Formula 28:

where Y is a tetravalent aromatic organic group or aliphatic organicgroup, and Z is a bivalent aromatic organic group or aliphatic organicgroup; and X of Formula 27 is a repeating unit of Formula 29:

where Y′ is a tetravalent aromatic organic group or aliphatic organicgroup, Z′ is a tetravalent aromatic organic group or aliphatic organicgroup, each of j and k is independently an integer from 1 to 6, and R₁is one of —OH, —SO₃H, —COOH, and —OPO(OH)₂; each of m and n isindependently from 30 to 5000; and the ratio of m to n is from 2:8 to8:2.